(a) Field of the Invention
The present invention relates to a piezoelectric actuator and a method for manufacturing the same, and more in particular to a piezoelectric actuator employed in an ink jet type recording apparatus mounted in a printer, a facsimile, a copier and the like and having high strength and reliability, and a method for manufacturing the same.
(b) Description of the Related Art
In an ink jet printer (hereinafter referred to as an ink jet recording apparatus), a piezoelectric actuator is usually employed in an ink head for ejecting ink. A conventional piezoelectric actuator is disclosed in JP-A-8(1996)-156272 and JP-A-8(1996)-118623. The conventional piezoelectric actuator will be described referring to the annexed drawings and reciting JP-A-8(1996)-156272.
FIG. 1A and FIG. 1B are perspective views showing the respective steps of a process of manufacturing a conventional piezoelectric actuator. In order to manufacture the conventional piezoelectric actuator, at first, a pair of piezoelectric element plates 28 are bonded to a substrate 14 along electrode patterns 26, 27 (refer to FIG. 1A).
Then, slits having a required pitch in the direction perpendicular to the longitudinal direction of the piezoelectric element plates 28 are formed on the piezoelectric element plate 28 and on the surface of the substrate 14 to make piezoelectric element rows 31 consisting of a plurality of piezoelectric elements (driving column) 29, 30 for separating the electrode patterns 26, 27 into individual electrodes 33 corresponding to each of the piezoelectric elements 29 (refer to FIG. 1A).
Edge electrodes (external electrodes) made by connecting every other internal electrode are formed on the both edge surfaces of the piezoelectric elements 29, 30 of the respective piezoelectric element rows 31. One external electrode on the edge surface is connected to the common electrode which the internal electrode on the substrate through the electroconductive material, and the other edge electrode is connected to the individual electrode 33 on the substrate through the electroconductive material. A support member 34 is bonded of which a height is nearly the same as those of the piezoelectric elements 29,30 on the periphery of the piezoelectric elements 29,30. The layered piezoelectric elements 29,30 outputs the displacement in the direction the same as that of the layers by means of the piezoelectric effect.
FIGS. 2A, 2B and 2C are a perspective view, a plan view and a side elevation view showing the state of the above piezoelectric element plate 28 taken out with the substrate 14, respectively. Conventionally, slit-like grooves 37 are formed in the direction perpendicular to the longitudinal direction of the piezoelectric element plate 28 to form a plurality of piezoelectric elements. Each piezoelectric element 29,30 is a long and narrow rectangle so that a pressure chamber formed thereby has a long and narrow shape. The displacement output surface 36a of each piezoelectric element 29,30 has the active region 36b formed by the crossing between the layers of the common electrode 32 and the individual electrode 33 which are the internal electrode and the inactive electrode extending to the side surface of the piezoelectric actuator connected to the external power and having either of the common electrode 32 or the individual electrode 33.
The output displacement produced on the active region 36b has a problem such that the output displacement decreases or becomes unstable because the displacement is restricted by the inactive region 36c. Since the slit-like grooves are formed by a dicing process using a thin cutting blade, the sectional shape of the groove is nearly rectangular, and a crack or a cutting due to bending is likely to occur at the corners of the groove bottom surface or the bottom parts of each piezoelectric elements 29,30. A further problem arises that the cost of manufacturing the piezoelectric actuator is high because the groove processing and the formation of the external electrode require a high cost.
It is necessary, in view of the above situation, to realize a piezoelectric actuator for an ink jet recording apparatus capable of generating an output displacement at high efficiency and stability by employing a shape having a narrowed part and a tapered part to elevate the strength and the reliability of a driving column in place of the rectangular displacement output surface and its rectangular section. It is also necessary to realize a piezoelectric actuator having excellent productivity by decreasing a processing cost of the slit-like groove separating and forming the piezoelectric actuator and of the external electrode.